Patent GB-250644-A (GB)
Title: Improvements in or relating to telephone exchange systems
IPC: H04Q3/42
Filed: 1925-01-08
Abstract: 250,644. Western Electric Co., Ltd., (Deakin, G.). Jan. 8, 1925. Automatic exchange systems; metering. - A link circuit provided at one end with means for finding the calling line and at the other end with means for selecting a wanted trunk, has associated with it two registers which jointly apply marking potentials to a wanted group of trunks in such a manner that the outgoing test relay is only connected up when the wanted group of trunks is engaged. In the system shown, a calling line is connected bv first and second line. finders 1LF, Fig. 1, 2LF, Fig. 2, to a link circuit which terminates at its right-hand end in a number of junction finders JF. Associated with the link circuit are two registers RG1, RG2, which are set in response to the first two digits, which may correspond to an exchange prefix, and mark the fourth and fifth contacts of all the trunks of a wanted group. The wipers of the junction finders JF are normally disconnected from the link circuit, but when a finder arrives on the first line of the marked group, a relay J1 - - J4 connected to the fourth and fifth wipers is energized over the marked contacts and connects up the line wipers of the finder which has found the trunk group and connects a common outgoing test relay JT1 to the test wiper. Provision is made for calling a local main exchange by dialling a single digit 1. In accordance with the office code the link circuit may be extended to junctions leading direct to wanted manual exchanges as described in Specification 250,642, or to local junction circuits whereby a call is extended to a wanted exchange through an intermediate exchange as described in Specification 250,643. Metering is effected by a booster impulse sent over the holding wire from a wiper P of the first register RG1 as this register passes through its last ten positions on returning to normal when the calling party hangs up. Line finders ILF, Fig. 1, and 2LF, Fig. 2. Upon a subscriber removing his receiver to make a call, a line relay L, Fig. 1, places a selectable potential on the fourth contact d, and energizes a common starting relay FS, which energizes a group of line finder starting relays AS, which in turn close circuits for the power magnets P of a group of first line finders ILF. When the calling line is engaged, test relay LT is energized over its high-resistance winding, opens the driving circuit, and closes a circuit for a holding relay LH in series with a common starting relay CS for the second line finders. Relay LH shunts the high-resistance winding of test relay LT with its low-resistance winding, marks the calling line busy, and shunts relay FS to arrest the finders. In the case of a simultaneous test by two line finders, both test relays pull up and energize their holding relays. The low-resistance windings of two test relays are unable to hold up these relays if two are connected in parallel to the same test terminal and both tend to fall away. As one will relapse slightly before the other, the one which relapses first will not energize over its high-resistance winding since the low resistance winding of the other relay remains connected up. The common starting relay CS energizes a group starting relay BS, which closes the circuits of the power magnets P1, Fig. 2, of a group of second line finders. When the first finder ILF is engaged by a second finder 2LF, a stopping relay ST1 is energized over the fourth wiper d, arrests the switch, and energizes a test relay JT2, which connects up the low-resistance winding of relay ST1 to mark the first finder busy, and energizes impulse relay IS over its right-hand winding. Relay IS closes a circuit for release relay R1, which energizes relay R2 and completes a circuit for switching relay A, holding winding of relay LH, Fig. 1, and the cut-off relay CO. Relay CO causes the relapse in turn of the relays L, LT, ST1, JT2. Relay A connects the two windings of the impulse relay IS respectively to the two line wires, whilst relay R2 closes a circuit for the dialling tone interrupter DTI over wiper O of the first register RG1. Setting of registers RG1, RG2 and operation of junction finder JF. Relapses of the impulse relay IS corresponding to the first digit energize the driving magnet of the first register RG1 in series with a slow-release relay C which relapses on the cessation of these impulses and closes a circuit for a change-over relay D over wiper O of the first register. Relay D locks up independently of relay C and directs the next impulse series to the second register RG2. The positions of the brushes R, W of the two resisters determine the junction group to be selected. The fifth and fourth contacts of all the wanted group of junctions are respectively strapped together and the contacts engaged by the brushes R, W are connected over a jumpering frame XR to the strapped fifth and fourth marking contacts. When the second register RG2 leaves its normal position, the power magnets PA, PB of all the junction finders JF associated with the link are energized, and the finders begin hunting for the marked junction group. A circuit is also closed over wiper T for a switching relay B, which locks up, disconnects the impulse relay IS, and connects up a supervisory relay S1, which now holds up release relay R1. When a junction finder JF engages the first junction in the wanted group, its connecting relay J1 - - J4 energizes over the fourth and fifth wipers and the register wipers W, R, and connects up the line and test wipers, completing a test circuit for the outgoing test relay JT1. On an idle junction being engaged, the test relay JT1 energizes, opens the driving circuits, and closes a circuit for a second test relay JT2, which connects up the low resistance winding of the first test relay JT1 to mark the engaged trunk non-selectable and energises a switching relay TO, which locks up over offnormal brush O of the register RG1, and deenergizes relay D. If all the wanted lines are engaged, the finders continue to rotate until one falls idle, the relay J1 - - J4 relapsing as the brushes pass off the wanted group of lines. When the called party answers, a called line supervisory relay S2 is energized and closes a circuit for a meter-preparing relay SM1, which locks up over brush O of the first register. Metering and release. When the calling party hangs up, relays S1, R1, R2 relapse, the lastmentioned relay closing restoring circuits over off-normal brushes N, S for the registers. In positions 11 to 21 of the register RG1, booster current is connected over brush P and the holding wire c to operate the meter SM, Fig. 1. In the normal positions of the registers the relays TC, SM1, Fig. 2, LH, CO, Fig. 1, are de-energized. Local main exchange call by dialling single digit 1. The register RG1 is advanced to its first position, after which the change-over relay D energizes as before, and closes a circuit over brushes S and Q for the register RG2, which is also advanced to its first position. The group of junctions to the local exchange is thereby marked and the link is extended to an idle one as described in the previous paragraph.